"Together they flew to New York City to confront the executive officers of Citicorp with the dilemma. "I have a real problem for you, sir," LeMessurier said to Citicorp's executive vice-president, John S. Reed. The two men outlined the design flaw and described their proposed solution: to systematically reinforce all 200+ bolted joints by welding two-inch-thick steel plates over them."
In the interview with Bill LeMessurier it seemed the problem existed even with the original joins - the bolted joins just made the issue significantly worse...
"The building now stands as one of the safest skyscrapers in New York City, able to withstand a 700-year storm without the aid of the tuned mass damper."
 Approximately 140mph gusts. http://civil.unm.edu/classes/content//CE%20491-002/ASCE%207-...
In particular, the 8-story-high diagonal parts were done in multiple splices that were supposed to be welded together but ended up being bolted together. It sounds like it made things much worse.
The builders did not notify the designers of the change, and 114 people were killed as a result.
The thing is, that design would have been a horrible pain to build as designed. It's a design failure. To build it, you'd need to slide a large steel section up two screws, following it by a nut up 30 feet. It needed to be redesigned by someone who knew more about fabrication and erection, and then checked closely to make sure that there weren't material changes in the performance.
This is fascinating, but I feel that I'm missing some terminology and concepts. I wonder if you could explain in more detail and clarify the terms?
From the part I do understand, it reminds me a lot of what I've encountered in a recent software project or two.
A company hires a visual design consulting firm for hundreds of thousands of dollars, and boy do they get their money's worth. Beautiful images and designs, complete with high quality videos with things moving all over the place in the smoothest and most seamless way.
And not a thought toward how this fantastic beautiful design would actually be implemented. No consultation with the programmers to see what could actually work given the required technology.
Agile? That's for programmers. When it comes to the product design, the visual designers have spoke, and that is that. It's waterfall time, baby!
On one project the designers decided it would be beautiful to have menus and controls that would slide out and overlap a Google Earth plugin. Great idea! Until you realize that it would take three solid months to work out all the cross-platform bugs in that approach. Three months that could have gone into building something useful, something that customers actually cared about.
When I worked as a CAD operator for a company which fabricated glass doors and windows, I would often receive printed drawings from architects. Soft copies were not available, as the architects considered their designs to be proprietary. But of course we the fabricators would benefit from having the design in CAD so we could produce different views and so on.
One day I received a set of drawings for a three-dimensional arrangement of glass sort of like a bay window. There were plan (overhead) and elevation (side) views, and I stared at those for a while, unable to make a coherent 3D model to match them. I then took some cardboard and cut it out in the shapes shown on the drawings. The shapes did not actually fit together--any way you tilted the pieces, there would be unworkable gaps in some part.
This was at the time when a lot of drawings were still made in 2D, with manual work to align the different views. I ended up having to visit the other firm's office, my cardboard cutouts in hand, to show them that what they had drawn could never be built.
So, the atrium was (say) 80 feet tall, with the sky bridges every 20 feet. So one at 20, 40, and 60 feet. If the continuous rod that had been specified in design was used, it'd be a little longer than 60 feet long (80 foot ceiling, lowest bridge 60 feet below that, plus a another foot or so to make room for fasteners).
That would mean that the middle bridge would have to have had the nuts spun along 40 feet (either from the top or bottom) and the nuts for the topmost and bottom-most bridge would have to be spun along 20 feet of thread. But before you could put the topmost nut on, you'd have to support the rod as you placed it through the box-section beams for the middle bridge. And then do the same for the topmost beam. And then lift it all so that the top end of the rod could be secured to the ceiling.
And this wouldn't have been one rod at a time -- you'd have to do the same for all dozen or more rods at the same time. Nightmare from a construction schedule standpoint.
1. There may be problems with that approach. IANAPE. They would be different problems than actually caused the failure.
I did a version in plain text and they ended up offering me a job.
This mean in Brazil there is a lack of experienced and honest engineers (the scumbag ones know how to not get shafted, the honest ones go to other countries, and the non-experienced ones... well, more meat for the grinder).
Earlier in May, LeMessurier met for an inquiry on another job where he mentioned the use of welded joints in the Citicorp building, only to find a potentially fatal flaw in the building's construction: the original design's welded joints were changed to bolted joints during construction, which were too weak to withstand 70-mile-per-hour (113 km/h) quartering winds. While LeMessurier's original design and load calculations for the special, uniquely designed "chevron" load braces used to support the building were based on welded joints, a labor- and cost-saving change altered the joints to bolted construction after the building's plans were approved.
Base of the Citigroup Center
View from the street
The engineers did not recalculate what the construction change would do to the wind forces acting on two surfaces of the building's curtain wall at the same time; if hurricane-speed winds hit the building at a 45-degree angle, there was the potential for failure due to the bolts shearing. The wind speeds needed to topple the models of Citigroup Center in a wind-tunnel test were predicted to occur in New York City every 55 years. If the building's tuned mass damper went offline, the necessary wind speeds were predicted to occur every 16 years.
> Resonant vibrational modes due to vertical loads (such as trains, traffic, pedestrians) and wind loads are well understood in bridge design. In the case of the Millennium Bridge, because the lateral motion caused the pedestrians loading the bridge to directly participate with the bridge, the vibrational modes had not been anticipated by the designers. The crucial point is that when the bridge lurches to one side, the pedestrians must adjust to keep from falling over, and they all do this at exactly the same time.
It's more precise to say "accounted for most dominant resonance modes".
Many catastrophic "accidents", and I use quotes because they could have been averted had people not cut corners w/o knowing the full context.
* Chernobyl (after hours test by an untrained crew with an inverted fail safe design)
* http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse (design change in the field, very similar to the citicorp flaw)
* 3 Mile Island (indicator that triggered on switch rather than valve)
* Fukashima (cost cutting on seawall and generator snorkels)
* Ariane-5 (code reuse, dead code)
Too many people don't design with proper safety factors. You build it, you test it, you test it till it fails and you understand those failures. I would trust another citicorp wouldn't happen because we can do realistic wind model, we can do an earthquake model, an anything model. Maybe we can get to a safety factor of 1 when everything is automated, when everyone has an off-site backup of their own brain but until then. Safety factor 6.
Of course, the advantage of that is that it hasn't collapsed yet, like a few under-engineered bridges built way later (http://www.washingtonpost.com/wp-dyn/content/article/2007/08...)
But I doubt the ones paying for the Brooklyn Bridge would have chosen this design if they could have had something for half the price that would last for 75 years.
Most modern bridges (and buildings, for that matter) get designed for 75, maybe 100 years of life. I don't think that is different in Europe. Older ones that still stand typically are sturdier, partly due to the use of larger safety margins by engineers who (according to today's knowledge) didn't know much about materials science, partly due to natural selection (bad designs collapsed or were taken down decades ago)
For every centuries old bridge, scores have been demolished because they couldn't handle increased traffic or just became too expensive to operate. And that happens in Europe, too, even in old-stuff loving Great Britain (http://en.wikipedia.org/wiki/London_Bridge)
Looking at bridges, I think the only ones that will stand for centuries are stone and masonry ones, and those rarely are built anymore. It is way easier to get large spans using reinforced concrete or steel. Both contain metal that rusts. Preventing that is expensive; fully preventing it probably prohibitively so. Even for landmarks bridges such as the Firth of Forth the Brits do not aim for eternal life (http://en.wikipedia.org/wiki/Forth_Bridge#Maintenance: "Network Rail has estimated the life of the bridge to be in excess of 100 years. However, this is dependant [sic] upon NR’s inspection and refurbishment works programme for the bridge being carried out year on year")
Let's consider the Golden Gate Bridge as an extreme example (extreme because lots of traffic across it has no reasonable alternative routes). If we needed to replace it, we could build a replacement bridge next to it, connect roads, and then open them over a weekend with little disruption.
If we chose to shove the new bridge in place of the old one in a week or so, that would have to disrupt traffic, but I doubt it would be more expensive than building _and_paying_for_ 20+ piers instead of the two we have _now_ (looking at http://en.wikipedia.org/wiki/List_of_longest_masonry_arch_br..., we cannot build masonry spans over 100m. The arch bridge is the best we can hope for when using stone because stone isn't strong in tension).
Also, such a disruption, announced years in advance, need not be that much of a disruption. People will take a few days of, stay with friends or family, maybe a temporary camp will be set up, etc)
On the other hand, that Wikipedia page mentions that many 50m+ stone arches have been built in China since 1950.
One: most of them are not impressive from a structural point of view. Two: most of them have been retrofitted so many times that they're hardly the "original" structure.
They were overbuilt because they didn't have the tools to estimate and calculate loads well, and didn't have alot of choice in materials. Essentially the choices were wood trusses or masonry arches.
I agree with you about lifespan -- look at New York's Tappan Zee bridge as an example -- it's a major traffic corridor, with a bridge with a lousy 50 year lifespan. Replacement will cost something like $10 billion!
1. I didn't even mention my nationality.
2. Right in my post I explained, why growing up in Europe might change perspective, since we're surrounded by old structures still in use.
3. To extend on this point: I do believe that the thinking here is a bit different when it comes to longevity of buildings. Hence why most homes here are made out of bricks or concrete with heavy foundations and a cellar, while the typical American home seems to be built out of wood and doesn't have a cellar. The abundance of land is probably heavily factoring into this, so more people can afford to buy land and build a house on it.
 E.g. Switzerland, my home country, has a home ownership of only 34% vs. 67% in the USA.
The Bridge started carrying train traffic 6 years after it opened so I am not sure today's loads are any lighter.
The original design with the welded joints would have allowed the building to withstand the corner winds, but it was replaced by bolts because builders thought it was overkill. Perhaps the consensus (or law?) should be to build with at least 2-3 times the calculated resistance, with only some justified exceptions.
Buildings would cost way more, but Intuitively it wouldn't be a bad thing (they would last longer and they would a bit less of a "mine's bigger" attitude)
No combination of factors approaches anything near what you would call a safety factor of 6. Typically things are designed with an analogous safety factor of 2.5 or less.
This isn't to say that higher factors of safety aren't possible, it's just that they're not worthwhile. We can design for anything. We just can't pay for it most of the time.
It also reminds me of the Mars Climate Orbiter. http://en.wikipedia.org/wiki/Mars_Climate_Orbiter
Apparently it costed $8 million to repair.
I'm sure the CCTV building is safe, but I get a small panic attack just thinking about walking or jumping up and down in that overhanging corner of the building.
How did they fix it? The article says they "welded" but doesn't say what was added to increase the strength of the building.
This is much more comprehensive and interesting than the source linked in OP and elsewhere.
I discovered this a few years back while doing some reading for an ethics class, and was fascinated by it.
The elevators are double-deckers. So the elevator actually has two rooms that move together. In the morning if you want to go to an even floor you have to enter from the basement level and if you want to go to an odd floor you have to enter from the lobby level. This results in the weird sensation that if you are going to a higher floor the elevators often stop but the doors do not open. Probably related to the weird design the elevators break down often and with or without an elevator set out of commission there are high queue times during peak hours. This is a building that could REALLY benefit from an elevator call system where you enter a floor and it assigns you which elevator to get into to. Why they haven't installed a relatively simple fix like this is beyond me.
My final gripe about this building is its sheer ugliness IMHO. The steel facade pegs it as one of those buildings that was built in a particularly time. It's not timeless like the Empire State Building or perpetually modern like the Willis Tower or One World Trade center.
I guess its only redeeming factor is the very nice public plaza it has both inside and outside, its direct access to the E and 6 trains (super convenient for me), and the fact that it has not fallen down yet.
It was fun to see the premise turn up in the show and go, oh, I think I know where they got this idea from.
> For the next three months, a construction crew welded two-inch-thick steel plates over each of the skyscraper's 200 bolted joints during the night, after each work day, almost unknown to the general public.
Out of morbid curiosity, what's the worst case scenario for something like this? Let's assume terrorists could detonate a bomb large enough to knock over any one skyscraper in the world. Where should they put it to maximize the chain reaction of destruction?
Sure you could have move the church, but where would you put it? It's in downtown Manhattan. You could probably find space pretty far away, but it's unlikely church members would stay members.
Where in the Bible do they demand masonry construction and a lack of elevators?
From an engineering standpoint that is a pretty depressing read.